This invention generally relates to an improved process for making certain cationic monomers. More particularly, this invention relates to an improved process for preparing N-substituted acrylamide monomers having cationic substituents attached thereto.
Cationic monomers are desired for preparing water-soluble cationic polymers useful in a number of applications, particularly in water treatment. Many cationic monomers are available and a variety of cationic polymers result directly therefrom or by suitable modification of these polymers. In certain applications including water treatment, cationic polymers must be resistant to hydrolysis in order to provide the properties for which their cationic character is chosen. A particularly desirable class of cationic monomers for making such polymers are those described as N-substituted acrylamides having cationic substituents. These monomers and their preparation are currently well known in the art.
In U.S. Pat. No. 3,878,247 issued Apr. 15, 1975 to P. H. Moss and R. M. Gipson, there is described a non-catalytic process for the preparation of N(tertiaryaminoalkyl) acrylamides which comprises subjecting a corresponding betaaminopropionamide to a temperature of about 180.degree.-300.degree. C. and separating the N-(tertiaryaminoalkyl) acrylamide from the reaction product. It also discloses that the corresponding aminopropionamide compounds can be made by reacting at least two moles of a tertiaryaminoalkyl amine with an acrylic acid or ester compound. The process is said to provide the desired compounds in high yields with minimal back-addition or polymerization.
The reference process thermally cracks a betaaminopropionamide to provide one mole of the desired monomer and one mole of tertiaryaminoalkyl amine for each mole of beta-aminopropionamide cracked. Such processing requires extremely harsh reaction conditions to be employed and theoretically restricts the amount of desired product that can be produced in a reaction vessel during a batch reaction to one mole of cationic monomer per mole of beta-aminopropionamide charged, although in actuality somewhat less than this amount is recovered.
An alternative method for producing cationic monomers, such as cationic methacrylamide, known in the art is the thermal decomposition of N-(dialkylaminoalkyl)-2-methylbeta-alanine. As described in U.S. Pat. No. 3,652,671, issued to Barron in 1972, this process proceeds through a rearrangement mechanism by heating the starting materials to between 140.degree.-230.degree. C.
Accordingly, there exists the need for a process which can provide a greater quantity of the desired cationic monomer per reaction given equimolar amounts of beta-aminopropionamide under milder reaction conditions and without the need for the recycling of reaction products. Such a provision would fulfill a long-felt need and constitute a significant advance in the art.